1. Field of the Invention
The present invention relates to a novel conjugate having cytotoxicity and a process for the preparation thereof. More particularly, the present invention relates to a novel conjugate having cytotoxicity comprising a constituent part consisting of an immunoglobulin capable of binding selectively to a particular antigen possessed by a cell to be killed (hereinafter referred to as a target cell) or consisting of its fragment having a part which binds to such antigen and a constituent part consisting of a serum albumin having a cytotoxic substance linked thereto and a process for the preparation of such a conjugate. The conjugate having cytotoxicity obtained according to the present invention is useful, for instance, as an antitumor agent which exerts an action on cancer cells selectively.
2. Description of the Prior Art
Studies and attempts have hitherto been made to bind cytotoxic substances of various kinds to an immunoglobulin, which is capable of binding selectively to a target cell, with the purpose of destroying certain kinds of cells selectively. For instance, a conjugate comprising an immunoglobulin having p-bis(2-chloroethyl)amino-L-phenylalanine, etc. linked thereto (Japanese Patent Application Laid-open No. 61640/76), a conjugate comprising an immunoglobulin having methotrexate linked thereto (Japanese Patent Application Laid-open No. 65829/81), a conjugate comprising an immunoglobulin having chlorambucil, etc. linked thereto (Japanese Patent Application Laid-open No. 65828/81), a conjugate comprising an immunoglobulin having mitomycin C, etc. linked thereto (Japanese Patent Application Laid-open No. 92325/80), and a conjugate comprising an immunoglobulin having daunomycin linked thereto (Japanese Patent Application Laid-open No. 144723/76) are known.
These conjugates having cytotoxicity obtained according to the abovementioned methods are expected to bind selectively to a cancer cell and exert a toxic action on the cancer cell and accordingly may be regarded as very useful conjugates. However, in case where the cytotoxic substance is directly bound to the antibody, if a large amount of cytotoxic substances is bound to the immunoglobulin, the activity of the antibody to recognize the antigen tends to become low. Therefore, only a small amount of cytotoxic substance has to be bound to the antibody to avoid such a problem.